It is known in modern emissions controlled automotive engines to place the metering of exhaust gas recirculation (EGR) under the control of an engine management computer. This has often been accomplished in an analog manner using an axially movable pintle valve. A linear solenoid, energized by the computer, withdraws the valve from the seat while position feedback is provided by a resistive potentiometer. The flow of recirculated exhaust gas is a function of the position of the valve above its seat.
While these systems have performed well in numerous applications, they have a number of disadvantages which are inherent to the concept. One disadvantage is that a sensor must be provided to indicate the valve position to the electrical control module (ECM). Also, a sophisticated closed-loop control algorithm is required to maintain a desired valve position. Both of these introduce undesired cost and complexity into the system.
A second factor is that the valve utilized is generally a more or less conical pintle operating in a circular seat. To expose lateral area equivalent to that of the circular hole, the stroke of the valve must be about half the hole radius, as much as a few millimeters in an automotive EGR valve. Since the size and mass of the linear solenoid is a direct function of the required stroke, the solenoid for this type of EGR valve tends to be quite bulky and massive. If a particularly large amount of EGR flow is needed, the solenoid may become unacceptably large.
Other types of EGR valves which have been proposed also involve additional materials, complications or control problems that may add to their cost or operability.